1. Oct 17, 2013 #1

   qedigiv

   

   If we are looking further and further back in time when we look at more and more distant galaxies, then how do we know that they are accelerating (instead of that they were accelerating a long long time ago)??

    

   qedigiv, Oct 17, 2013
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3. Oct 17, 2013 #2

   mfb

   

   Insights Author

   2017 Award

   Staff: Mentor

   You can look at galaxies everywhere from "now" to ~13 billion years ago. This allows to get the current velocities as well as the velocities in the past.
   You don't see the same galaxies as they are now and as they were 13 billion years ago, of course, but if you see the current velocity of galaxies nearby you can extrapolate this to get the current velocity of more distant galaxies.

    

   mfb, Oct 17, 2013

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